1. Field of the Invention
The present invention relates to a car data transmission device equipped with optical fiber cables.
2. Discussion of Background
As a car data transmission device using optical fibers, a construction as shown in FIG. 1 is considered in which transmission lines are looped in two rows through a series of cars.
In FIG. 1, a transmission controlling device 2 which transmits and receives optical signals is installed in each car 1. The optical signals transmitted from the transmission controlling device 2 is passed through a optical fiber line 3 to be received in a subsequently connected transmission controlling device 2. In the FIG. 1, arrow marks indicate the direction of transmitting optical signals. Generally, only one looped line is used to send data in the duplex transmission lines and the other is for a spare system.
In case of the transmission line system shown in FIG. 1, if one of the two lines is broken, reconstruction of the transmission system is made by utilizing the other line to continue data transmission.
FIGS. 2 and 3 show examples in which a separate transmission path is constituted by reconstructing the duplex line system when the main transmission line is broken.
FIG. 2 shows that the inner looped line is broken at a point 4 and the duplex line system is reconstructed to use the outer looped line. FIG. 3 shows that both lines are broken at points 7,7 and the system is reconstructed to use a looped transmission line as shown by the dotted line in the transmission controlling devices 2.
In the duplex transmission line system, there may be constructed in such a manner that a single optical fiber cable is used for the connecting part between cars and all optical fiber lines passed between the cars are received in the optical fiber cable. FIG. 4 shows an example of such construction in which the reference numeral 8 designates optical fiber cables for gathering the optical fiber lines into one unit and 9 designates jointing optical fiber cables used as joints between the cars. In the construction shown in FIG. 4, if a jointing cable between the cars is cut to be separated, the duplex transmission lines are entirely broken and it is no longer possible to reconstruct the transmission lines.